1. Field of the Invention
The invention relates to a control apparatus/method for an internal combustion engine having a supercharger connected to an intake passage and driven by a motor.
2. Description of the Related Art
An attempt to provide an intake passage of an engine (internal combustion engine) with a motor-driven supercharger and to achieve a high output (or low fuel consumption) through supercharging performed by the supercharger has generally been made. Such an internal combustion engine is disclosed also in Published Japanese translation of a PCT application JP-T-2001-518590. In the internal combustion engine disclosed in Published Japanese translation of a PCT application JP-T-2001-518590, an intake passage is bifurcated into two branch flow passages, which are combined into one flow passage again. A supercharger driven by a motor is connected to one of the branch flow passages. A combined portion of the branch flow passages is provided with a switching valve that changes the branch flow passage from which intake air flows toward the downstream side. When the supercharger is operated, the switching valve opens the branch flow passage that is provided with the supercharger, and closes the branch flow passage that is not provided with the supercharger. On the contrary, when the supercharger is not operated, the switching valve closes the branch flow passage that is provided with the supercharger, and opens the branch flow passage that is not provided with the supercharger. In this manner, while the supercharger is prevented from causing a loss in intake air, the backflow of intake air is prevented.
The state of switching valve in the internal combustion engine disclosed in Published Japanese translation of a PCT application JP-T-2001-518590 mentioned above is changed in accordance with a difference between a pressure in each of branch pipes on the upstream side and a pressure in an intake pipe on the downstream side. If the switching valve is designed to make use of a differential pressure as described above, the state of the switching valve may be inappropriately changed and the flow of intake air may pause for a moment. For example, if the supercharger is stopped from performing supercharging, the state of the switching valve is changed after stoppage of the supercharger, and then the flow of air is generated in the branch pipe that is not provided with the supercharger. At this moment, the flow of intake air pauses, and the internal combustion engine may be operated discontinuously.